Extracellular matrix (ECM) molecules such as fibronectin (FN) and laminin (LN) are restricted in their spatial and temporal expression. They have important influences upon cellular proliferation, differentiation and mobility. Antibodies to LN will inhibit key lung developmental processes like branching morphogenesis. A more recently described ECM molecule, tenascin (TN), also has a restricted spatio-temporal expression in mammalian lung. It may modulate the binding of cells to ECM substrates like FN and it can induce fibroblast metalloproteinase genes such as collagenase. My hypothesis is that cell-extracellular matrix interactions regulate pulmonary branching morphogenesis and alveolarization; I propose that TN is an ECM molecule which has a major role as a regulator of lung development and that inhibition of TN expression may be important in the response of the developing lung to postnatal injury. Using in vitro and in vivo methods we will investigate two key periods of lung development: Aim 1. Branching morphogenesis a) Determine the spatio-temporal expression of tenascin, including its alternatively spliced forms, in lung by morphologic measures at light and electron microscopic resolutions. b) Measure lung TN gene and protein expression. c) Test the functional importance of TN upon branching morphogenesis with polyclonal anti-TN antiserum and with monoclonal domain-specific anti-TN antibodies and recombinant expression proteins. d) Test whether interactions of tenascin with laminin and fibronectin modify adherence and spreading of fetal lung fibroblasts and epithelial cells on plastic substrate. Aim 2. Alveolarization: We will use autoradiography to measure cell kinetics of the lung parenchyma. Alveolar septal cellular proliferation will be compared to the spatio- temporal expression of lung tenascin. Completion of these specific aims will extend our current work on cellular kinetics and ECM structural molecules of growing lung. Previously identified milestones of lung epithelial development will be correlated with epithelial-mesenchymal interactions to be studied with this support. Understanding of mechanisms leading to bronchopulmonary dysplasia will be advanced.